The present invention relates to a method and a system for evaluating qualities of articles such as electric/electronic apparatuses for home use, products for office-automation (OA) and the like which are manufactured by assembling constituent parts. More particularly, the present invention is concerned with a fraction defective estimating method for estimating likelihood of occurrence of failure in the works involved in assembling an article, a system for carrying out the fraction defective estimating method and a storage medium storing therein data, information and program for executing the method.
Methods known heretofore for determining the fraction defective are primarily so designed as to estimate the causes for occurrence of defects, failures or the like, starting from the defect events or failure phenomena which have actually taken place. As the hitherto known typical methods of estimating the cause of failure or detect on the basis of the contents of the failure phenomenon or the defect event actually or really taken place at a stage in the course of manufacturing process, there may mentioned those disclosed in Japanese Unexamined Patent Application Publication No. 167631/1989 and Japanese Unexamined Patent Application Publication No. 196900/1994. These methods are based on such techniques that real records of defects occurred in the past are stored together with data concerning the causes of such defects in order to allow a degree of correlation between a defect pattern and the cause for the defect to be determined, whereon the cause for the defect is estimated on the basis of the correlation as determined. Further, as the diagnosis techniques in which the similar techniques are adopted, there may be mentioned those disclosed in Japanese Unexamined Patent Application Publication No. 13617/1995 and Japanese Unexamined Patent Application Publication No. 271587/1995.
However, any one of the known methods mentioned above is directed to the technique for estimating directly the causes of defect events or failure phenomena on the basis of the contents of such defects or failures which have really taken place for the purpose of allowing correcting or repairing work to be carried out speedily and properly.
On the other hand, as a method or procedure for performing in advance a quality evaluation of an article to be manufactured before failure or defect really occurs, there is known an FMEA (Failure Mode and Effects Analysis) technique which can already be adopted in the stage of designing the article to be manufactured. According to this method, an evaluator himself or herself predicts xe2x80x9cfailure phenomena which may occur in relation to individual parts constituting an articlexe2x80x9d and summarizes the xe2x80x9cfailure phenomena or events together with relations to the individual parts in the form of a list. Thus, by referencing the list, the evaluator himself or herself can predict xe2x80x9cwhat sort of influence the article as manufactured will suffer when certain failure(s) or defect(s) occursxe2x80x9d. In this way, high-quality design suffering substantially no unintentional omissions can be realized.
Further, there is known a method or procedure for estimating seriousness of defects or failures relating to individual parts, respectively, by determining the probability of occurrence of failure phenomenon in relation to the individual parts as estimated by the evaluator (which probability is termed the fraction defective) and then estimating the degree of seriousness of defect of an article as manufactured which can be considered as being ascribable to the defect(s) of the individual parts. As a typical one of such techniques, there may be mentioned FMECA (Failure Mode, Effects and Criticality Analysis) technique.
However, any one of the conventional methods or techniques mentioned above is not in the position to estimate the potential of detector failure to occur in a given article with high accuracy. This is because substantially all the failure phenomena which may actually occur have to be grasped in the case of the conventional methods.
Under the circumstances, not a few manufacturing failures actually take place due to insufficiency of examination or studying, presenting one of the factors for deterioration of the quality of the manufactured article.
In the light of the art described above, it is an object of the present invention to provide a method and a system for estimating the potential of occurrence of failure in assembling a given article already in the stage preceding to manufacturing process, e.g. at a stage of design, manufacturing process planning or the like.
At this juncture, it should be mentioned that with the term xe2x80x9cpartxe2x80x9d used herein, it is contemplated to encompass both an elementary part and an assembled part or subassembly constituted by a plurality of the elementary parts. Accordingly, with a phrase xe2x80x9cpart attaching workxe2x80x9d, it is intended to encompass both the attaching works not only for an elementary part but also an assembled part, respectively. Further, an elementary part or an assembled part which is to be attached to another elementary part or assembled part will be collectively referred to as xe2x80x9cattachment-destined partxe2x80x9d while the latter which is subjected to or undergoes the attachment will be referred to as xe2x80x9cattachment-subjected partxe2x80x9d.
In view of the above and other objects which will become apparent as the description proceeds, it is taught according to the present invention that an estimated value of assembling-related fraction defective which indicates likelihood of occurrence of defectives in an assembled article is determined on the basis of information concerning factors which exert influence to the probability of occurrence of failure in relation to the operations which are involved in part attaching works and which can not always be performed by a worker without fail. (The probability mentioned above will hereinafter be referred to also as the uncertainty.)
In a preferred mode for carrying out the invention, the estimated value of the assembling-related fraction defective is arithmetically determined on the basis of information concerning the contents of operations involved in part attaching works, information concerning properties of an attachment-destined part or parts and information concerning properties of an attachment-subjected part or parts.
To this end, according to an aspect of the present invention, species or types of operations required for expressing the contents of the operations involved in the part attaching works (such as operation for downward movement, operation for horizontal movement and the like which are correctively referred to as standard attaching operation) are determined, and numerical values indicating low or high probabilities that standard attaching operations can not be performed without fail under predetermined conditions inclusive of xe2x80x9ccondition imposed by an operator or worker, condition imposed by a part and conditions imposed by a work-shopxe2x80x9d (these conditions will be referred to as basic conditions) is determined or set for each of the standard attaching operations as determined. (The numerical values mentioned above will be referred to also as the standard-attachment-operation-based fraction defective coefficient.)
In another mode for carrying out the invention, an object under evaluation is expressed in terms of a combination of preset standard attaching operation elements for the purpose of facilitating user interface.
Furthermore, according to another aspect of the present invention, it is taught with a view to enhancing the estimation accuracy of the assembling-related fraction defective that in addition to the aforementioned standard attaching operation elements used for expressing the contents of attaching operations involved in the part attaching work, properties of the attachment-destined part and the attachment-subjected part which exert influence to the uncertainty of the attaching operation are expressed in terms of part-condition-related supplementary factors mentioned below, whereon the estimated value of the assembling-related fraction defective is arithmetically determined on the basis of the part-condition-related supplementary factors. More specifically, the factors exerting influence to the uncertainty of attaching work performed by a worker among the properties of the attachment-destined part and the attachment-subjected part (these factors are referred to as the part-condition-related supplementary factors) are determined, whereon for the part attaching work for an object for which the assembling-related fraction defective is to be estimated, those part-condition-related supplementary factors which are relevant to the properties of the attachment-destined part or attachment-subjected part in the part attaching work of concern are selected from the preset part-condition-related supplementary factors mentioned above for expressing the contents of the attaching operation in addition to the expression given in terms of combination of the standard attaching operations as mentioned above.
According to another aspect of present invention, it is taught with a view to enhancing further the accuracy in estimating the assembling-related fraction defective that for the part attaching work in assembling an article for which the fraction defective is to be estimated, information indicating whether a step or process for confirming if the part attaching work of concern has been performed correctly and properly is provided or not in succession to the assembling work process is used in addition to the standard attaching operation elements expressing the contents of attaching operation involved in the part attaching work and the part-condition-related supplementary factors giving influence to the uncertainty of the attaching operation, for thereby arithmetically determining the estimated value of the assembling-related fraction defective.
According to a further aspect of the present invention, it is taught with a view to enhancing further the accuracy in estimating the assembling-related fraction defective that the estimated value of the assembling-related fraction defective is arithmetically determined on the basis of a numerical value (referred to as the shop constant) indicating degree of influence of the shop conditions and reflecting the factors exerting influence to the uncertainty of the attaching operation such as the condition imposed by the worker, the condition imposed by equipment installed in the assembling shop, environmental condition and the like for the part attaching work in addition to the standard attaching operation elements expressing the contents of attaching operation involved in the part attaching work, the part-condition-related supplementary factors exerting influence to the uncertainty of the attaching operation and the information indicating whether a step or process for confirming if the part attaching work of concern has been performed correctly and properly is provided or not in succession to the assembling work process.
According to a still further aspect of the present invention, it is taught that the fraction defective coefficients each for each of the individual standard attaching operations of the attachment-destined part, the supplementary coefficients each for each of the properties of the attachment-destined parts and the supplementary coefficients each for each of the properties of the attachment-subjected parts are stored in advance, wherein the information representing the combination of predetermined standard attaching operations for expressing an object under evaluation and the information representing the properties of an attachment-destined part and the attachment-subjected part of the object under evaluation are inputted, whereon the fraction defective coefficients for the standard attaching operations of concern, the relevant supplementary coefficient for the attachment-destined part and the relevant supplementary coefficient for the attachment-subjected part are extracted from the inputted information, to thereby arithmetically determine the assembling-related fraction defective of the object under evaluation by adding together the values resulting from supplementation of the individual fraction defective coefficients as extracted with the supplementary coefficients for the attachment-destined parts and those for the attachment-subjected parts.
According to a yet further aspect of the present invention, there is provided a fraction defective estimating system which includes a means for storing fraction defective coefficients each for each of individual standard attaching operations for attachment-destined parts, supplementary coefficients each for each of properties of the attachment-destined parts and supplementary coefficients each for each of properties of attachment-subjected part, a means for inputting information representing a combination of predetermined standard attaching operations for expressing an object under evaluation as well as information representing the properties of the attachment-destined parts and the attachment-subjected part of an object under evaluation, and a means for extracting the fraction defective coefficient for the standard attaching operation of concern, the relevant supplementary coefficient for the attachment-destined part and the relevant supplementary coefficient for the attachment-subjected part from the inputted information, to thereby arithmetically determine an assembling-related fraction defective for the object under evaluation by adding together values resulting from supplementation of the individual fraction defective coefficients as extracted with the supplementary coefficients for the attachment-destined parts and those for the attachment-subjected parts.
Furthermore, according to the present invention, there is provided such arrangement that when fraction defective coefficients for every standard attaching operation for attachment-destined parts, supplementary coefficients for every property of an attachment-destined part, supplementary coefficients for every property of attachment-subjected parts, information representing a combination of predetermined standard attaching operations for expressing an object under evaluation and the information concerning properties of the attachment-destined parts and the attachment-subjected part constituting the object under evaluation are inputted, fraction defective coefficients for relevant standard attaching operations, supplementary coefficients relating to the attachment-destined part and supplementary coefficient relating to the attachment-subjected part are extracted from the input information, for thereby arithmetically determining an assembling-related fraction defective of the object under evaluation by adding together values obtained by supplementing the extracted individual fraction defective coefficients with the supplementary coefficients relating to the attachment-destined part and those relating to the attachment-subjected parts. The procedure described above can be executed by a computation unit with the aid of a program designed properly to this end.
In this conjunction, it is preferred to store previously the supplementary coefficients for every number of attachments to be carried out for thereby arithmetically determining an assembling-related fraction defective by supplementing the aforementioned fraction defective coefficient with the supplementary coefficient relating to the number of attachments required in realizing the object under evaluation, or store previously a supplementary coefficient corresponding to presence or absence of a process for confirming whether the attachment-destined part has been properly attached to the attachment-subjected part, for thereby arithmetically determining an attachment-related fraction defective of the object under evaluation by supplementing additionally the fraction defective coefficient with the corresponding supplementary coefficients in the case where there exists the process for confirming whether the attachment-destined part has been properly attached to the attachment-subjected part.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.